1. Field of the Disclosure
The present invention relates generally to electronic amplifiers, and more specifically to electronic amplifiers that set a maximum value of an output signal.
2. Background
Electronic circuits often use operational amplifiers to process analog signals. An operational amplifier is a convenient building block for circuits that modify analog signals in a particular way, such for example changing amplitudes, filtering frequency components, or performing linear mathematical operations that may include summing with other signals, integrating, and differentiating.
Operational amplifiers typically can produce output voltages that approach the value of their power supply voltages. In many applications, it is desirable to limit the value of an output signal from an operational amplifier so that the output will remain within the acceptable range of input values for circuits that receive the output signal. It is generally good design practice to limit the magnitudes of signals to be within a range that guarantees controlled and reliable operation. Designers have devised clamping circuits that use diodes at the input or at the output of the operational amplifier to keep the output from exceeding a desired limit.
Known clamping circuits that use diodes can introduce undesirable characteristics and behavior that result from the switching of the diodes. A diode at the input can make the input impedance nonlinear and dependent on the magnitude of the signal. A diode on the output may block a large excursion of the output signal in one direction to the power supply voltage, only to allow a transient overshoot when the output recovers in the opposite direction.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.